Binders for fibrous materials, such as fiberglass, have a variety of uses ranging from stiffening applications where the binder is applied to woven or non-woven fibrous sheet goods and is cured, producing a stiff product; thermoforming applications wherein the binder resin is applied to a sheet or lofty fibrous product, following which it is dried and optionally is B-staged to form an intermediate but yet curable product; and to fully cured systems such as building insulation.
Fiberglass insulation products generally comprise matted glass fibers bonded together by a cured thermoset binder. The rigid thermoset polymer matrix ensures that a finished fiberglass insulation product, when compressed significantly for packaging and shipping, recovers to its labeled thickness when installed in a building.
Due to the excellent cost/performance ratio, phenol-formaldehyde binders have been widely used in fiberglass insulation products. However, phenol-formaldehyde binders emit a substantial amount of formaldehyde during the curing process and finished products can off-gas formaldehyde after being installed. Because of the existing and proposed legislation on lowering or eliminating formaldehyde, extensive efforts have been directed to replace formaldehyde-based binders with formaldehyde-free binders.
One type of these formaldehyde-free binder compositions rely on esterification reactions between carboxylic acid groups in polycarboxy polymers and hydroxyl groups in alcohols. Water is the main byproduct of these covalently crosslinked polyesters, which makes these binders environmentally benign. However, reaction rates for these compositions are generally slower than for formaldehyde-containing systems, which can reduce production rates for materials incorporating these binders.
Additionally, the slower reaction rates and more polar reaction compounds in the formaldehyde-free binders can have deleterious effects on the final products made with these compositions. The slower reactions rates can result in less crosslinking in the final binder, which can reduce the mechanical strength of composite products that include the binder. The more polar reaction compounds are usually more hydrophilic, resulting in increased water absorption by the binder in the final product. When the final product is exposed to humid environments, the increased water absorption can significantly shorten the lifetime of the material. Thus, there is a need for new formaldehyde-free binder compositions that provide improved mechanical strength and/or water resistance (among other properties) to the final product. This and other issues are addressed in the present application.